Boiler maker Volume 11

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ...pipes are damaged seriously. To avoid this the internal pipe should, when discharging above the water level, be turned upwards at the end, so as to always remain filled with water, and when turned downward to discharge under the water the end should be well below the lowest working level. An additional means of safety is sometimes afforded by fitting inside the boiler a clack or check valve, so arranged as to close over the end of the intemal pipe or on the spigot of the ordinary check valve. /Vhen this is provided the latter can be examined when steam is up. A blow-off cock should be fitted at or near the bottom of the boiler, to answer the double purpose of admitting sea-water before getting up steam and to blow off some of the water when required. This cock should be a very strong one, as it is liable to rough usage, and being out of sight and not easily got at it is very apt to be neglected. For this reason, as well as because a large cock is difificult to open and shut, some engineers prefer a valve to a cock. If a cock is fitted it should be so arranged that the handle or spanner cannot be removed when it is open. The clear area through a blow-off cock should be = 1 square inch + 0.2 square inch for each ton of water in the boiler. As it is a very reprehensible practice to quickly blow off a marine boiler when at its normal working temperature, a somewhat smaller cock is fitted to the bottom of the boiler, so that when the pressure of the steam is down to about 20 pounds the water may be blown into the sea through the ordinary cock until the level is just above the furnace crowns; it is then allowed to remain and to cool down with the boiler and finally emptied into the bilge through this cock. i A scum cock, having a clear area through it of one-thir...